A cheap tang sight can be OK for general playin' around, but if you want real repeatability in adjustments between ranges and changes you are going to have to pay some good money. Take a look a
www.buffaloarms.com to see a fine selection of sights, but get prepared for sticker shock.
As to mounting, depending upon the sight's base length and how it will ride on the wrist, you want the lower eyecup position to still be usable so position for it. Taping a base on to mock-up and all is worthwhile.
You do want the underside of the base to be supported out to the edges to avoid any rocking side to side; its better to scrape the top of the wrist to achieve this than file or grind the base.
You want the staff to go vertical to the gun, otherwise as you adjust elevation you change windage.
Once in a satisfactory position you can screw it straight onto the wrist; inserts are tidy, but not necessary. Be aware the the buttstock throughbolt hole is in there. For most wood I like screws with parallel threads, rather than tapered threads. Once you have proven the position and function in use you may want to consider installing the inserts. I can assure you it is much easier to nicely plug, fill and color match the woodscrew holes in the wrist than the larger insert holes, should you ever want to.
Some will tell you that mounted straight onto the wrist will have changes due to humidity, etc. Well, no-one I know ever goes to a match without sighting in again anyway, so no worries.
Some will tell you that it is not as strong as tang mounted, etc. True, so what, either way you do not want to be bouncing your rifle off the tang sight anyway.